Oven-circulating air type



July 26, 1932. A. E. GRAPP OVEN CIRCULATING AIR TYPE Filed Sept. 5, 1930 2 Sheets-Sheet l July 26, 1932. A. E. GRAPP OVEN CIRCULATING AIR TYPE Filed Sept.

5, 1930 2 Sheets-Sheet 2 Invenifar hisfl r s MMMM W fee Patented .July 26, 1932 ALBERT E. GRAPE, OF MINNEAPOLIS, MINNESOTA 'ovnn-cmcunarme Am ma Application filed September 5, 195m. Serial no. 479,898.

This invention relates to ovens and furnaces adapted for various uses, such as, for example, heat treatment of steel, drying and baking coated surfaces, etc.

It is an object of my present invention to provide a highly eflicient oven or furnace for pr educing substantially uniform distribuvtion of heat throughoutthe heating chamber, operative with a high degree of economy and because of its structure, effective to bring the heating chamber and its contents rapidly {1p to the desired temperature. I ore specifically it is an object to provide an oven or furnace wherein air and/or hot gases are continually circulated through the heating chamber, means being provided for removing a small portion of the air and other gases as the same are re-circulated and for supplying an equal and small amount of fresh air simultaneously.

Still another object is to' provide an oven of the type described wherein the burners or heating elements are disposed in the lower portion of the oven, heating the air within the oven by radiation and convection through a conductive bottom and wherein a forced circulation of heated air is set up through the heating chamber. the air flowing through passages or venturi between the heating chamber and the oven housing and entering the end the heating chamber opposite from the conductive bottom.

Another object is to provide in an oven of the type described having a fan and motor for driving the same, means for coolingthe shaft and bearings of said motor by a sucp tion of-air adjacent the bearing and shaft due to the efiect of the fan within the oven.

These and other objects and advantages of.

the invention will be fully set forth in the following description made in connection with the accompanying drawings, in which like reference characters refer to similar parts throughout the several views, and in which Fig.1 is a front ment of my invention with the oven door v closed adequate oxygen elevation of an embodi-.

Fig. 3 is'a vertical section taken on the line 33 of Fig.1, and

Fig. 4 is a vertical section taken on the line 44 of Fig. 2. i

In the embodiment of the invention illustrated in the drawings a relatively thick rectangular box-like housing H is provided which may comprise inner and outer metal jackets 5 and 6 respectively, between which is disposed a heavy layer of heat insulating or 00 refractory material 7. The housing includes top, bottom and side walls and a doorway 8 is formed in the front wall having mounted therein a heavily insulated hinged door 9.

Within housing H is a'rectangular heating 66 chamber '10 spaced from the top, bottom an side walls of the housing and defined by a box-like preferably metal casing having vertical side walls 11 which are spaced from the innner side walls of the housing and extend from the rear wall to the front wall thereof. Heating chamber 10 is provided with a top 12 having a relatively large central aperture wherein a'suitable fan 13 is disposed. A bottom for the heating chamber is provided as shown at substantially the lower end of the doorway by means of a conductive plate 14 having up-tnrned vertical side flanges 14a which are disposed medially between the vertical walls llof the heating chamber and the respective adjacent inner walls 5 of the housing, flanges 14a extending some distance above the lower edges of walls 11.

Heating elements may be mounted in the bottom of housing H below the conductive 55 late 14 and while it will be understood that any suitable type 'of heating element may be employed, in the form illustrated I dlsclose a pair ofgas burners 15 having orifices directed upwardly towards conductive bottom or plate 14. Burners 15 may extend horizontally and inwardly from the front wall of the housing and'openings 16 in said front wall are provided for supplying to the burners, the size of said openingsif desiredbeing controllable by vertically sliding doors 17 mounted in suit able guides. Burners 15 are mounted at the top of burner boxes 18 which as shown,

have inturned horizontal flanges 18c spaced a slight distance from 'thepipe or burner proper 15 topermit a supply of oxygen for aiding combustion.

The fan 13 at the upper end of the heating chamber may be fixed to a depending shaft 19 which as shown constitutes the projection of the armature shaft of an electrical motor M. Motor M is mounted centrally above the top of housing H with its lower end spaced therefrom to permit free access of air beneath the motor and around shaft 19. A central vertical passage or opening is formed through the top of housing H and an inverted funnel-shaped tube 20 1S fixed in said opening concentrically surrounding shaft 19 and with its open upper end disposed just below the motor M and havin therein a series of apertures 20a to permit lateral passage of air into said tube. The lower or flared end of tube 20 is open and terminates just above the central portion of fan 13. The plates of fan 13 are so skewed or turned that their inner ends at the center of the fan produce a displacement of air causing a strong suctionthrough the tube 20.

At the rear of the heating chamber 10 a contiguous vertical duct 21 is provided having an elbow 21a communicatin with its lower end and which under-lies t e bottom of the heating chamber formed h conductive plate 14. A relatively small air discharge passage 22 is formed through the bottom plate 14 communicating with the elbow 21a.

If desired, two series of oppositely disposed ledges lla may be provided on the walls 11 of the heating chamber adapted to support reticulated shelves 12 on which articles, to be heated may be placed. Several articles A, such as metal castings are illustrated in Fig. 4 of the drawings, which may be placed in the oven for heat treatment, such as for example, tempering or case-hardening.

A gas supply pipe 23 is shown on the ex erior of the housing H communicating tldgrough valves 24 with the burner conduits A suitable thermostatically operated heat regulator may be provided for my oven in cluding an electro-magnetically operated valve for controlling the gas supply to pipe 23, which mechanism, however, forms no part of my present invention and therefore is not illustrated or described in detail.

Operation In operation a hot flame is generated by each of the burners 15, the particular structure of the burner with reference to the burner boxes 18 setting up a nice draft ofair around the burner conduits. The rapid rotation of fan 13 sets up a circulation of air throughout the oven as clearly indicated by the arrows in the drawings. The hot products of combustion which are of relatively small volume pass upwardly between flanges 14a of the conductive bottom and the inner side walls 5 of the housing and air is drawn from the heating chamber 10 downwardly, most of said air passing outwardly and then upwardly between the flanges 14a and the side walls 11 of the heating chamber. The re-circulated air and hot products of combustion pass upwardly in the venturi or passages between the heating chamber and side walls of the oven and enter the top of the heating chamber through fan 13.

In the circulation of the hot air a small amount is exhausted through the discharge aperture, 22 in the center ofbottom plate 14, this discharged air passing through elbow 21a and duct 21.

The inner ends of the fan blades 13 are so skewed that the centralportion of the fan will displace or draw a small amount of air through the funnel tube 20 into the-top of the heating chamber. This downwardly directed suction draft of air is taken from adjacent the lower bearing of motor M and through the lateral ports 20a in the upper and projected end of tube 20. The incoming air cools the said motor bearing and shaft 19 which, being constructed of conductive desired point by transmission, convection and radiation of heat.

From the foregoing description it will be seen that a very uniform temperature will be maintained throughout the entire heating chamber. The provision of a conductive bottom for the heating chamber which is subjected to the intense heat of the burner flames in combination with the circulating fan at the upper or opposite end of the heating chamber is responsible for the highly successful results in securing a uniform distribution of heat. The entire heating cl1amber is preferably constructed of heat conductive material, such as metal, and is quickly brought up to a high temperature by the impingement of the hot circulating air and the hot products of combustion against the walls llthereof. These walls and the inner ovens where a draft of air is passed laterally across the heating chamber.

It will further be noted that the heat from the small volume of vapor and steam as well contrasted with other types of circulating air 7 59 externally of said heating chamber and communicating with the two ends of said chamoutwit-lathe heating efi'ect produced by the direct i tails, proportions producln g as carbon dioxide and other products of combustion is not wasted by passa e into a stack or flue, but is admixed with t ere-circulated air in the. venturi between walls 1 and the inner side walls of the housing.

The total area of the air passages or discharges at the lower end of the heating chamber, includingmthe upwardly directed passages formed tween walls 11 and upturned flanges 14a and also discharge aperture 22 is less than the area of the centrally disposed relatively large air intake passage at the top of the heating chamber wherein the fan 13 is mounted, as will be apparent from the drawings. This causes some pressure to be built up in the heating chamber due to the forced circulation of air-,and in the embodiment disclosed this pressure is approximately +1. The building up of this relatively small pressure materially aids the even distribution of temperature and heated air throughout the entire heating chamber and heat of the conductive bottom 14' of the chamber, careful tests have shown that throughout the entire heating chamber a uniform temperature is obtained.

From the foregoing description it will be seen that I have invented a comparatively simple, compact and highly efiicient oven a substantially uniform distribution of heat throughout the heating chamber and operative wlth a high degree of economy due to the recirculation pr'inci leand consumption of heat from the pro nets of combustion of the burners.

It will, of course, be understood that various changes may be made in the form, de-

and arrangement of the parts, without departin from the scope of applicants invention, w ich, generally stated, consists in a device capable of carrying out the ob ects above set forth and in the novel parts and combinations of parts disclosed and defined in the appended claims.

-What is claimed is 1. An oven comprising a heat insulated housing, a heating chamber disposed in said housing and spaced from one end thereof,

air passages extending longitudinally and her, a fan mounted in an opening in one end of said heating chamber, a fan motor mounted externally upon the adjacent end of sa1d housing with an extension of its armature shaft projected into said housing and carrying said fan and'a relatively small air intake passage throughsaid end of said housing and surrounding the extension of said shaft whereby fresh air will be drawn about the inner end and bearin 'of said motor impinging against (said sha t. t

2. The structure set forth in claim 1 wherein said air intake passage constitutes an inverted funnel-shaped tube, the outeropen end ofwhich is provided with lateral air intake ports adjacent the bearing of themotor and the'inner and flaring endof which terminates adjacent the center of said fan. 7

3; An oven comprising, a heat insulated housing, a heating chamber constructed of heat conductive material disposed in said from at least two of the housing and spaced I thereof as well as from vertical inner walls the top and bottom of said housing, said space between said chamber and said housing forming passages for the circulation of air, a fan mounted in an openingin'the upper end'of said heating chamber and adapted to project the heated air downwardly through said'chamber, air outlet passages through t e lower end of said heating chamber and communicating with the air passages between the vertical walls'of said housing and said chamher, said chamber having a conductive bottom plate, burners mounted beneath said bottom plate having orifices directed against said plate, horizontal burner boxes communieating at their .ends with the outside air and having inturned longitudinal flanges extending parallel with and in close spaced relation to the sides of said burners.

4. In an oven, a vertical housing, a vertical heating chamber, mounted in said housing and spaced from at least two of the vertical walls of said housing as well as from said housing to form passages for the circulation of air, a relatively large air intake passage in the in said housing and spaced from at least two of the vertical walls of said housing as well as from the top of said housing to form a passagefor the circulation of air, said heat ing chamber having a heat conductive bottom, heating elements disposed below said bottom-for directly heating the same and for heating by conduction and radiation the air the'top oftop ofsaid heating chamber, a 7 fan mounted in said passage for forcing air' bottom and adjacent the in the bottom of said heating chamber, said.

heating chamber having an air intake passage in the upper end thereof and air outlet passages in the bottom thereof, said outlet passages communicating with the passages defined by the spaced vertical walls of said chamber and said housing, a fan for setting up a forced circulation of air downwardly through saidheating chamber and upwardly In testimony whereof I afiix my signature.

-ALBERT E. GRAPP. 

